System for removing alcamines in NMP (N-Methyl Pyrrolidone) recovery liquid

Abstract

The invention discloses a system for removing alcamines in NMP (N-Methyl Pyrrolidone) recovery liquid. The system comprises a dehydration rectifying tower, a reaction separation tower, a product refining tower and a reaction and reaction separation tower reboiler which is used as a reactor, the dehydration rectifying tower is respectively connected with the reaction separation tower and the product refining tower; the reaction and reaction separation tower reboiler is connected with the reaction separation tower; the reaction and reaction separation tower reboiler is connected with a dehydration rectifying tower or a product refining tower; the reaction and reaction separation tower reboiler comprises an outer heat exchange tube; an inner reaction heat exchange tube is arranged in the outer heat exchange tube; the inner reaction heat exchange tube is an inner enhanced heat exchange tube; the reaction and reaction separation tower reboiler is provided with an inner side tube plate for separating a shell pass of the reaction and reaction separation tower reboiler from an outer heat exchange tube pass and an outer side tube plate for separating the outer heat exchange tube pass from an inner reaction surrounding tube pass. The method realizes high yield, fast reaction rate and energy-saving removal of alcamines in NMP.

Description

Technical Field

[0001] This invention relates to the fields of new energy and environmental protection, and in particular to a system for removing alkanolamines from NMP. Background Technology

[0002] In lithium-ion battery systems, during the preparation of precursors for positive or negative electrode materials, alkanolamines (such as ethanolamine, diethanolamine, and triethanolamine) are commonly used in solution chemistry to synthesize metal oxide or phosphate-based positive electrode materials (such as LiFePO4 and NMC). They can act as complexing agents, binding with metal ions and controlling the concentration balance of metal ions in the solution, thereby influencing crystal growth and particle size distribution, which is beneficial for obtaining more uniform electrode active material particles with controllable particle size. Furthermore, in the slurry preparation process (such as the preparation of electrode coating slurries), alkanolamines can be used as dispersants or viscosity modifiers, helping particles in the slurry to be more uniformly distributed and stably suspended, improving coating uniformity, and thus improving the quality of the finished electrode.

[0003] N-Methylpyrrolidone (NMP) is an important chemical solvent characterized by low toxicity, high boiling point, strong dissolving power, good selectivity, and good stability. It is the most commonly used solvent in the production of metal-ion batteries. NMP is miscible with water, PVDF, positive and negative electrode materials, and is therefore widely used in lithium battery manufacturing. When making electrode sheets, NMP acts as a solvent to fuse various electrode materials such as binders, positive electrode active materials, and conductive agents together, ensuring that the binder is in full contact with other materials and is evenly distributed.

[0004] The current standard process flow in the market is as follows: A slurry of electrode material (a mixture of lithium nickel cobalt manganese oxide, conductive carbon black, solvent NMP, binder PVDF, and additives) is uniformly coated onto both sides of an aluminum foil. A closed negative pressure exhaust dryer (drying channel) is used. After coating, the positive electrode is baked and dried in a vacuum dryer to remove solvents such as NMP and some alkanolamine additives from the electrode. The dried solvent gas enters a solvent recovery unit to obtain a recovered solvent containing N-methylpyrrolidone, trace amounts of alkanolamine additives, trace amounts of water, and high-temperature decomposition and recombining components.

[0005] The boiling points of NMP (at atmospheric pressure) are: 204℃, ethanolamine: 170℃, diethanolamine: 271.1℃, triethanolamine: 335.4℃, propanolamine: 187.5℃, and isopropanolamine: 159.5℃. Based on these data, ethanolamine, propanolamine, and isopropanolamine have lower boiling points than NMP, and are therefore separated as light components in the distillation column relative to NMP. Diethanolamine and triethanolamine have higher boiling points than NMP, and are therefore separated as heavy components in the distillation column relative to NMP. Propanolamine is unique; under a negative pressure of 2 kPa, its boiling point is 96℃, while NMP's is 89℃. Under negative pressure distillation, it is separated as a heavy component in the distillation column relative to NMP.

[0006] For NMP recovery solutions typically containing amine additives at a mass fraction concentration of approximately 0.001–0.006%, the boiling points of diethanolamine, triethanolamine, and isopropanolamine differ significantly from those of NMP. With existing distillation units, acceptable NMP products can be obtained by modifying operating conditions. However, the boiling points of ethanolamine and propanolamine are too close to those of NMP, and the concentrations of amine additives are very low. Separating these small amounts of impurities through a distillation column requires a large amount of energy, and different amine additives result in different operating conditions for the distillation column, making it impossible to use a single, standardized system to accommodate the different additives.

[0007] With the development of the semiconductor industry, the requirements for free amines in NMP are becoming increasingly stringent, with some even requiring 1 ppm. Ordinary distillation methods can only achieve 20-30 ppm. This differs from NMP synthesis, which uses γ-butyrolactone and excess methylamine. Methylamine has a boiling point of -6.3℃, making NMP and methylamine relatively easy to separate. However, ethanolamine and propanolamine used in lithium battery production have boiling points close to NMP, making it difficult to control the free amine content below 30 ppm using only ordinary distillation processes and under low-energy conditions. Invention patent CN116239514A discloses a method for reducing free amines in NMP. This method involves adding acid to neutralize the material, bringing the pH value between 6.5 and 7.5. The neutralized material is then fed into a second dehydration tower for dehydration separation. This method involves acid-base neutralization, and the neutralized amine salts are discharged as heavy components at the bottom of the purification tower. However, ammonium salts still decompose during the reboiler heating process in the refining tower. Furthermore, the acids produced during decomposition accelerate the decomposition of NMP, leading to a decrease in the quality and yield of the NMP product. Additionally, the free amines generated during decomposition appear as light components in the NMP product, failing to meet the requirement of low free amine concentrations, such as 1 ppm.

[0008] Furthermore, ethanolamine and propanolamine are commonly used as additives in lithium battery production. To address this challenge, the inventors have proposed a method for removing ethanolamine, propanolamine, and other alcoholamines from the recovery solution using an anhydride reaction (such as maleic anhydride). Unlike invention patent CN116239514A, which uses an acid-base neutralization mechanism, the anhydride reaction is a subamidation reaction, resulting in more stable reaction products that do not decompose during high-temperature heating.

[0009] However, the reaction rate of acid anhydrides is currently slow under normal temperature conditions, and water in the recovered solution, as one of the reaction products, is detrimental to the reaction. The reaction of maleic anhydride to remove ethanolamine and propanolamine from NMP solution is an exothermic reaction, and the temperature of the reaction system has a significant impact on the conversion rate of reactants. When the reaction temperature is too low, the intermolecular collision rate is slow, and the reaction is difficult to occur. When the reaction temperature is too high, acid anhydrides are prone to hydrolysis (if the material has a high water content), and the alkene bonds in the acid anhydride molecules are also prone to self-polymerization, thus causing side reactions. In addition, ethanolamine or propanolamine will volatilize under negative pressure or low pressure conditions and high temperature, reducing the reaction yield. Therefore, reasonable control of reaction temperature and pressure is particularly important for the yield of this reaction.

[0010] In summary, there is a need to develop a production process that is high-yield, fast-reaction, and energy-efficient to remove free alkanolamines from NMP solvents. Summary of the Invention

[0011] The technical problem to be solved by the present invention is to provide a system for removing alkanolamines from NMP with high yield, fast reaction rate and energy saving.

[0012] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0013] By creating reasonable reaction conditions and adopting the principle of reaction-distillation coupling, a system for removing alkanolamines from NMP recovery liquid was developed, including a dehydration distillation column, a reaction separation column, a product purification column, and a reaction and reaction separation column reboiler as a reactor.

[0014] The dehydration distillation column is connected to the reaction separation column and the product purification column, respectively.

[0015] The reaction and reaction separation tower reboiler includes an external heat exchange tube;

[0016] The external heat exchange tube contains an internal reaction heat exchange tube.

[0017] The internal reaction heat exchanger tube is an internally enhanced heat exchanger tube;

[0018] The reboiler of the reaction and reaction separation tower is provided with an inner tube sheet separating its shell side and outer heat exchange tube side, and an outer tube sheet separating its outer heat exchange tube side and inner reaction surrounding tube side.

[0019] The external heat exchange tube of the reboiler of the reaction and reaction separation tower is connected to the reaction separation tower;

[0020] When ethanolamine is removed, the internal reaction heat exchange tube of the reaction and reaction separation tower reboiler is connected to the dehydration distillation tower;

[0021] When removing propanolamine, the internal reaction heat exchange tube of the reaction and reaction separation tower reboiler is connected to the product purification tower.

[0022] The beneficial effects of this invention are as follows: the dehydration distillation column removes water from the feed liquid, the product purification column removes heavy components from the feed liquid, the dehydration distillation column or product purification column increases the concentration of alcoholic amines in the feed liquid, and the reaction and reaction separation column reboiler reacts the alcoholic amines with acid anhydrides. The generated water and NMP are drawn from the top of the reaction separation column and returned to the dehydration distillation column for further dehydration. In the process of removing alcoholic amines from the NMP recovery liquid, the water content in the NMP recovery liquid is first reduced by the dehydration distillation column, and the content of alcoholic amines is increased, which is conducive to the efficient progress of subsequent reactions. Furthermore, an internal reaction heat exchanger is set inside the outer heat exchanger tubes of the reaction and reaction separation column reboiler (shell and tube heat exchanger). The internal reaction heat exchanger uses internally enhanced heat exchanger tubes. In addition to the inner tube sheet separating the shell side and the outer heat exchanger tube side of the heat exchanger, an outer tube sheet separating the outer heat exchanger tube side and the internal reaction heat exchanger tube side is also set. On the one hand, the initial internal reaction... The heat transfer from the material in the heat exchange tube to the material in the outer heat exchange tube facilitates the rapid reaching of the reaction temperature and accelerates the reaction rate. On the other hand, after the material in the inner reaction heat exchange tube reaches the reaction temperature, the heat generated by the reaction needs to be carried away by the material in the outer heat exchange tube. The inner enhanced heat exchange tube can increase the disturbance, making the temperature of the material inside the tube more uniform. Through the design of the reaction and reaction separation tower reboiler with the above-mentioned specific structure, it is beneficial to the heat transfer and temperature control inside and outside the tube. In addition, during the reaction process, the incompletely separated products after the reaction are introduced back to the dehydration distillation tower for further distillation through the reaction separator, and then introduced back into the reaction and reaction separation tower reboiler for further reaction through the dehydration distillation tower or product purification tower. This realizes a dynamic coupling process of distillation and reaction simultaneously, ensuring that the purity of the final product is relatively high. Thus, a system for removing alkanolamines from NMP with high yield, fast reaction rate and energy saving is achieved. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a system for removing ethanolamine from NMP recovery solution according to an embodiment of the present invention;

[0024] Figure 2This is another structural schematic diagram of a system for removing propanolamine from NMP recovery solution according to an embodiment of the present invention;

[0025] Figure 3 This is a schematic diagram of the structure of the reaction and the reboiler of the reaction separation tower according to an embodiment of the present invention;

[0026] Figure 4 This is another structural schematic diagram of the reaction and the reboiler of the reaction separation tower according to an embodiment of the present invention;

[0027] Figure 5 This is a schematic diagram of the internal and external heat exchange tubes of the reaction and reaction separation tower reboiler according to an embodiment of the present invention;

[0028] Figure 6 This is a schematic diagram of the structure of the support member for the internal and external heat exchange tubes according to an embodiment of the present invention;

[0029] Label Explanation:

[0030] S1~S40 and S101~S140, stream numbers; E1, first dehydration tower reboiler; E2, first dehydration tower condenser; E3, first dehydration tower vacuum collector; E4, first reaction separation tower condenser; E5, first reaction separation tower vacuum collector; E6, first reaction and reaction separation tower reboiler; E7, first product tower heat pump; E8, first product tower vacuum collector; X1, first dehydration tower feed static mixer; X2, first reaction feed static mixer; P1, first dehydration tower reflux. Pumps; P2, First dehydration tower heavy component discharge pump; P3, Dehydration tower side-stream discharge pump; P4, First reaction separation tower reboiler circulation pump; P5, First reaction separation tower reflux pump; P6, First product tower reboiler circulation pump; P7, First product tower heavy component discharge pump; P8, First product tower reflux pump; T1, First dehydration distillation tower; T2, First reaction separation tower; T3, First product refining tower; V1, First dehydration tower reflux tank; V2, First reaction separation tower reflux tank; V3, First product refining tower reflux tank; E 11. Second dehydration tower reboiler; E12. Second dehydration tower condenser; E13. Second dehydration tower vacuum collector; E14. Second reaction separation tower condenser; E15. Second reaction separation tower vacuum collector; E16. Second reaction and reaction separation tower reboiler; E17. Second product tower heat pump; E18. Second product tower vacuum collector; X11. Second dehydration tower feed static mixer; X12. Second reaction feed static mixer; P11. Second dehydration tower reflux pump; P12. Second dehydration tower refluxing pump. Component discharge pump; P13, Product tower side discharge pump; P14, Second reaction separation tower reboiler circulation pump; P15, Second reaction separation tower reflux pump; P16, Second product tower reboiler circulation pump; P17, Second product tower heavy component discharge pump; P18, Second product tower reflux pump; T11, Second dehydration distillation tower; T12, Second reaction separation tower; T13, Second product purification tower; V11, Second dehydration tower reflux tank; V12, Second reaction separation tower reflux tank; V13, Second product purification tower reflux tank. Detailed Implementation

[0031] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0032] The system described above for removing ethanolamines from NMP recovery solution is applicable to methods for removing ethanolamines and propanolamines from recovery solution using anhydride reactions (such as maleic anhydride). Specific embodiments are described below:

[0033] In one alternative implementation, please refer to Figure 1 (removal of ethanolamine) and Figure 2(Removal of propanolamine), a system for removing alcoholic amines from NMP recovery liquid, comprising a dehydration distillation column, a reaction separation column, a product purification column, and a reaction and reaction separation column reboiler serving as a reactor;

[0034] The dehydration distillation column is connected to the reaction separation column and the product purification column, respectively.

[0035] The reaction and reaction separation tower reboiler includes an external heat exchange tube;

[0036] The external heat exchange tube contains an internal reaction heat exchange tube.

[0037] The internal reaction heat exchanger tube is an internally enhanced heat exchanger tube;

[0038] The reboiler of the reaction and reaction separation tower is provided with an inner tube sheet separating its shell side and outer heat exchange tube side, and an outer tube sheet separating its outer heat exchange tube side and inner reaction surrounding tube side.

[0039] The external heat exchange tube of the reboiler of the reaction and reaction separation tower is connected to the reaction separation tower;

[0040] When ethanolamine is removed, the internal reaction heat exchange tube of the reaction and reaction separation tower reboiler is connected to the dehydration distillation tower;

[0041] When removing propanolamine, the internal reaction heat exchange tube of the reaction and reaction separation tower reboiler is connected to the product purification tower.

[0042] In another alternative implementation, such as Figures 3 to 6 As shown, a support is provided every 1m to 1.5m along the axial direction between the external heat exchange tube and the internal reaction heat exchange tube of the reaction and reaction separation tower reboiler, wherein the external heat exchange tube and the internal reaction heat exchange tube are arranged concentrically.

[0043] The support members are evenly distributed in the radial direction of the external heat exchange tube.

[0044] In an optional embodiment, the support is provided at 120-degree intervals in the radial direction of the external heat exchange tubes of the reaction and reaction separation tower reboiler.

[0045] In this embodiment, the use of a support member can prevent vibration between the external heat exchange tube and the internal reaction heat exchange tube.

[0046] In another alternative embodiment, the position where the support of the reaction and reaction separation tower reboiler contacts the external heat exchange tube is set in an arc shape.

[0047] In this embodiment, the area where the support member contacts the external heat exchange tube is designed as an arc, which can ensure that the internal reaction heat exchange tube and the external heat exchange tube can slide smoothly, facilitating installation and maintenance.

[0048] In another alternative implementation, there are two ways to achieve internally enhanced heat exchange tubes:

[0049] In the first implementation, the internal enhanced heat exchange tube of the reaction and reaction separation tower reboiler is an internally threaded enhanced heat exchange tube. The bottom wall thickness of the internally threaded tube is generally in the range of 0.25 to 0.3 mm, the tooth height is generally in the range of 0.1 to 0.2 mm, and the helix angle of the internally threaded tube is in the range of 15° to 25°.

[0050] In the second implementation, a spiral coil is inserted into the inner reaction heat exchange tube of the reboiler of the reaction and reaction separation tower. The spiral coil and the heat exchange tube are installed with a gap of 0.5 to 1 mm. A wire diameter of 0.6 to 1.2 mm and a spiral pitch of 5 to 10 mm are selected.

[0051] In another optional embodiment, it also includes a static mixer for feeding the dehydration tower, a reflux pump for the reaction separation tower, a condenser for the dehydration tower, a reflux tank for the dehydration tower, a reflux pump for the dehydration tower, and a discharge pump for the heavy components of the dehydration tower.

[0052] The top output of the reaction separation tower is connected to the input of the reaction separation tower condenser; the output of the reaction separation tower condenser is connected to the input of the dehydration tower reflux tank; the output of the reaction separation tower condenser is connected to the input of the reaction separation tower reflux tank; the gas phase output of the reaction separation tower reflux tank is connected to the input of the reaction separation tower vacuum collector; and the output of the reaction separation tower vacuum collector is connected to the vacuum system.

[0053] The liquid phase output of the reflux tank of the reaction separation tower is connected to the input of the reflux pump of the reaction separation tower, and the first output of the reflux pump of the reaction separation tower is connected to the top reflux input of the reaction separation tower. The second output of the reflux pump of the reaction separation tower is connected to the second input of the static mixer for the feed of the dehydration tower, and the output of the static mixer for the feed of the dehydration tower is connected to the input of the dehydration distillation tower; the top output of the dehydration distillation tower is connected to the input of the dehydration tower condenser, and the output of the dehydration tower condenser is connected to the input of the reflux tank of the dehydration tower.

[0054] The output end of the dehydration tower reflux tank is connected to the input end of the dehydration tower reflux pump;

[0055] The first output end of the dehydration tower reflux pump is connected to the top reflux input end of the dehydration distillation tower;

[0056] The first output end of the bottom of the dehydration distillation column is connected to the input end of the dehydration column heavy component discharge pump, and the output end of the dehydration column heavy component discharge pump is connected to the input end of the product refining column.

[0057] In this embodiment, in the dehydration distillation column, light components such as water accumulate at the top, and the separated water can be drawn off from the top. NMP and heavy components accumulate at the bottom, and the dehydrated material can be drawn off from the bottom and fed into the product purification column for further separation. Alkylamines fall into two categories: ethanolamines mainly accumulate in the upper section of the dehydration distillation column and can be drawn off via a side stream in the middle section, merging with the reactant (maleic anhydride) and entering the reaction heat exchange tubes in the reboiler of the reaction and separation column. Propanolamines mainly accumulate in the lower section of the product purification column and can be drawn off via a side stream in the lower section, merging with the reactant (maleic anhydride) and entering the reaction heat exchange tubes in the reboiler of the reaction and separation column. Through this process, the moisture content of the reactants decreases, while the content of alkylamines increases. By increasing the concentration of reactants, the probability of intermolecular collisions increases, which is beneficial for increasing the reaction rate and the concentration of reaction products, thereby reducing the energy consumption for subsequent separation. The water and imines produced by the reaction of acid anhydrides and alcoholic amines, water and most of NMP are drawn from the top of the reaction separation tower as light components and mixed with NMP waste liquid raw material before being sent to the dehydration distillation tower to remove water. The imines after the reaction, a small amount of NMP and other impurities are drawn from the bottom of the reaction separation tower as heavy components and discharged outside the boundary.

[0058] In another optional embodiment, it also includes a dehydration tower vacuum trap, a dehydration tower pressure controller, a dehydration tower vacuum system, a first regulating valve (pressure regulating valve), a dehydration distillation tower top sensitive plate temperature controller, a dehydration tower reflux flow controller, a second regulating valve (flow regulating valve), a dehydration tower reboiler, a dehydration distillation tower bottom sensitive plate temperature controller, and a third regulating valve (temperature regulating valve).

[0059] The second output end of the dehydration tower reflux pump is connected to the input end of the dehydration tower vacuum collector, and the output end of the dehydration tower vacuum collector is connected to the dehydration tower pressure controller and the dehydration tower vacuum system respectively through the first regulating valve (pressure regulating valve);

[0060] The first output end of the dehydration tower reflux pump is connected to the top reflux input end of the dehydration distillation tower. The temperature controller of the sensitive plate at the top of the dehydration distillation tower and the flow controller of the dehydration distillation tower respectively act as the main and auxiliary loops to adjust the opening of the second regulating valve (flow regulating valve), thereby completing the cascade control of the above variables and ensuring the purity of the product.

[0061] The second output end at the bottom of the dehydration distillation column is connected to the input end of the dehydration column reboiler;

[0062] The output end of the dehydration tower reboiler is connected to the reboiler input end of the dehydration distillation tower;

[0063] The temperature controller of the bottom plate of the dehydration distillation column is connected to the heat medium input terminal of the reboiler of the dehydration column through the third regulating valve (temperature regulating valve).

[0064] In this embodiment, the pressure of the dehydration distillation column can be well controlled by the cooperation of the vacuum trap of the dehydration column, the first regulating valve (pressure regulating valve), the pressure controller of the dehydration column, and the vacuum system of the dehydration column. The flow rate of the reflux liquid phase of the dehydration distillation column can be well controlled by the sensitive plate temperature controller at the top of the dehydration distillation column, and the flow rate of the heat medium added to the reboiler of the dehydration column can be well controlled by the sensitive plate temperature controller at the bottom of the dehydration distillation column.

[0065] In another alternative embodiment, it also includes a side-line discharge pump, a reaction feed static mixer, an online titrator, a reaction feed flow converter, a reaction feed flow controller, and a fourth regulating valve (flow regulating valve);

[0066] The side-stream output of the dehydration distillation column (for removing ethanolamine) or the side-stream output of the product purification column (for removing propanolamine) is connected to the input of the side-stream discharge pump. The output of the side-stream discharge pump is connected to the first input of the reaction feed static mixer. The reaction raw materials are connected to the second input of the reaction feed static mixer.

[0067] The detection point of the online titrator is connected to the pipeline between the output end of the side-line discharge pump and the first input end of the reaction feed static mixer. Based on the detection result, the reaction feed flow control system calculates the set value of the reaction flow rate, and adjusts the amount of input acid anhydride substances through the reaction feed flow controller and the fourth regulating valve (flow regulating valve).

[0068] The output end of the static mixer for the reaction feed is connected to the input end of the internal reaction heat exchange tube of the reboiler for the reaction and reaction separation tower, and the output end of the internal reaction heat exchange tube of the reboiler for the reaction and reaction separation tower is connected to the input end of the reaction separation tower.

[0069] In this embodiment, materials with low water content and high amine content are pressurized by a side-stream discharge pump (ethanolamine is discharged from the dehydration distillation column, and propanolamine is discharged from the product refining column). The amount of acid anhydride added to the reaction raw materials is controlled by an online titrator in conjunction with a reaction feed flow control system and a fourth regulating valve (flow regulating valve). This ensures that the amount of acid anhydride added is neither too much nor too little, thereby ensuring both the reaction rate and the feasibility of distillation.

[0070] In another optional embodiment, it also includes a fifth regulating valve (flow regulating valve), a reaction separation tower flow controller, a reaction separation tower top sensitive plate temperature controller, a reaction separation tower condenser, a reaction separation tower reflux tank, a separation tower vacuum trap, a separation tower pressure controller, a separation tower vacuum system, a sixth regulating valve, and a reaction separation tower reflux tank level controller.

[0071] The output end of the reaction separation tower is connected to the input end of the reaction separation tower condenser, and the output end of the reaction separation tower condenser is connected to the input end of the reaction separation tower reflux tank.

[0072] The first output end (liquid phase) of the reaction separation tower reflux tank is connected to the input end of the reaction separation tower reflux pump;

[0073] The second output end (gas phase) of the reaction separation tower reflux tank is connected to the input end of the separation tower vacuum trap, and the output end of the separation tower vacuum trap is connected to the separation tower pressure controller and the separation tower vacuum system respectively through the fifth regulating valve (flow regulating valve);

[0074] The sixth regulating valve (flow regulating valve) is connected between the second output end of the reflux pump of the reaction separation tower and the reflux input end at the top of the reaction separation tower. The temperature controller of the sensitive plate at the top of the reaction separation tower and the flow controller of the reaction separation tower respectively act as the main and auxiliary loops to regulate the opening of the sixth regulating valve, thereby completing the cascade control of the above variables and ensuring the purity of the product.

[0075] The liquid level controller of the reaction separation tower reflux tank is adjusted by the opening of the liquid level control valve, thereby controlling the liquid level of the reaction separation tower reflux tank.

[0076] In this embodiment, the pressure of the reaction separation tower can be well controlled by the cooperation of the separation tower vacuum trap, the fifth regulating valve (flow regulating valve), the separation tower pressure controller and the separation tower vacuum system, while the flow rate of the reflux liquid phase in the reaction separation tower can be well controlled by the temperature controller of the sensitive plate at the top of the separation tower.

[0077] In another alternative embodiment, it also includes a reboiler circulation pump for the reaction separation tower, a temperature controller for the sensitive plate at the bottom of the separation tower, and a seventh regulating valve (temperature regulating valve);

[0078] The bottom output of the reaction separation column is connected to the input of the reboiler circulation pump of the reaction separation column;

[0079] The output end of the reboiler circulation pump of the reaction separation tower is connected to the input end of the external heat exchange tube;

[0080] The output end of the external heat exchange tube is connected to the input end of the reaction separation tower;

[0081] The temperature controller of the sensitive plate at the bottom of the separation tower is connected to the heat medium input terminal of the reaction and the reboiler of the reaction and reaction separation tower through the seventh regulating valve (temperature regulating valve).

[0082] In this embodiment, the flow rate of the heat medium added to the reboiler of the reaction separation tower can be well controlled by the temperature controller of the sensitive plate at the bottom of the separation tower.

[0083] In another alternative embodiment, the reaction separation tower is packed with two layers of metal wire mesh packing.

[0084] The first filler layer from top to bottom is equivalent to 5 to 10 theoretical plates, and the second filler layer is equivalent to 5 to 10 theoretical plates.

[0085] When removing ethanolamine, the operating temperature at the top of the reaction separation column is 39–65°C, the operating temperature at the bottom of the column is 125–135°C, and the operating pressure at the top of the column is 1–5 kPa.

[0086] When removing propanolamine, the operating temperature at the top of the reaction separation column is 39–70°C, the operating temperature at the bottom of the column is 125–135°C, and the operating pressure at the top of the column is 1–5 kPa.

[0087] In another alternative embodiment, it also includes an eighth regulating valve (flow regulating valve), a refining column flow controller, a refining column top sensitive plate temperature controller, a product column heat pump, a product column reflux tank, a product column reflux pump, a product column vacuum trap, a product column pressure controller, a product column vacuum system, and a ninth regulating valve (pressure regulating valve).

[0088] The top output of the product refining tower is connected to the condenser input of the product tower heat pump, and the condenser output of the product tower heat pump is connected to the input of the product tower reflux tank.

[0089] The first output end (liquid phase) of the product tower reflux tank is connected to the input end of the product tower reflux pump;

[0090] The second output end (gas phase) of the product tower reflux tank is connected to the input end of the product tower vacuum trap, and the output end of the product tower vacuum trap is connected to the product tower pressure controller and the product tower vacuum system respectively through the ninth regulating valve;

[0091] The eighth regulating valve (flow regulating valve) is connected between the first output end of the product tower reflux pump and the top reflux input end of the product refining tower. The temperature controller of the sensitive plate at the top of the product refining tower and the flow controller of the product refining tower respectively act as the main and auxiliary loops to adjust the opening of the eighth regulating valve (flow regulating valve), thereby completing the cascade control of the above variables and ensuring the purity of the product.

[0092] The second output terminal of the product tower reflux pump outputs NMP finished product.

[0093] In this embodiment, the pressure of the product purification tower can be well controlled by the cooperation of the product tower vacuum trap, the ninth regulating valve (pressure regulating valve), the product tower pressure controller and the product tower vacuum system, while the flow rate of the reflux liquid phase in the product purification tower can be well controlled by the product tower top sensitive plate temperature controller.

[0094] In another alternative implementation, a product tower reboiler circulation pump is also included;

[0095] The output end of the product refining tower is connected to the input end of the product tower reboiler circulation pump;

[0096] The output end of the product tower reboiler circulation pump is connected to the heating input end of the product tower heat pump;

[0097] The heating output end of the product tower heat pump is connected to the reboiling input end of the product refining tower.

[0098] Depending on the type of alcoholic amines being removed, there are two methods for implementing dehydration distillation columns:

[0099] In the first implementation, the dehydration distillation column is filled with three layers of metal wire mesh packing. This implementation is used to remove ethanolamine from NMP recovery liquid.

[0100] The first packing layer from top to bottom is equivalent to 4 to 8 theoretical plates, the second packing layer is equivalent to 6 to 12 theoretical plates, and the third packing layer is equivalent to 10 to 24 theoretical plates.

[0101] The side feed outlet of the dehydration distillation column is connected to the input end of the side feed pump;

[0102] Correspondingly, the product refining tower is filled with two layers of metal wire mesh packing;

[0103] The first packing layer from top to bottom is equivalent to 5 to 10 theoretical plates, and the second packing layer is equivalent to 5 to 10 theoretical plates. The operating temperature at the top of the product refining tower is 85 to 105°C, the operating temperature at the bottom of the tower is 115°C to 130°C, and the operating pressure at the top of the tower is 2 to 4 kPa.

[0104] In the second implementation, the dehydration distillation column is filled with two layers of metal wire mesh packing. This implementation is used to remove propanolamine from the NMP recovery liquid.

[0105] The first filler layer from top to bottom is equivalent to 10 to 20 theoretical plates, and the second filler layer is equivalent to 10 to 20 theoretical plates.

[0106] The side discharge end of the product refining tower is connected to the input end of the side discharge pump.

[0107] Correspondingly, the product refining tower is filled with two layers of metal wire mesh packing;

[0108] The first packing layer from top to bottom is equivalent to 20 to 36 theoretical plates, and the second packing layer is equivalent to 20 to 36 theoretical plates.

[0109] The operating temperature at the top of the product refining tower is 75-95℃, the operating temperature at the bottom of the tower is 105-115℃, and the operating pressure at the top of the tower is 1-2.5 kPa.

[0110] In another optional embodiment, the operating temperature at the top of the dehydration distillation column is 39–46°C, the operating temperature at the bottom of the column is 130–135°C, and the operating pressure at the top of the column is 7–10 kPa.

[0111] The following examples illustrate the usage process of the system for removing alkanolamines from NMP waste liquid described in this application:

[0112] In this embodiment, the removal of ethanolamine from NMP waste liquid feedstock using maleic anhydride is used as an example for illustration:

[0113] A typical waste liquid contains 79.8% NMP, 19.6% water, 0.4% ethanolamine, and 0.2% heavy components by mass. In lithium battery coating processes, an NMP aqueous solution of approximately 80% is common, while the ethanolamine mass fraction is typically 0.1%–0.4%. However, the apparatus of this invention does not strictly limit the specific component values; all components can be produced using the process of this invention. The entire system requires nitrogen or other inert gas for protection to prevent the oxidative decomposition of NMP.

[0114] The process is illustrated below using the typical waste liquid example described above:

[0115] like Figure 1As shown, the feed stream S1 and the stream S21 from the outlet of the reflux pump P5 of the first reaction separation tower are mixed in the static mixer X1 of the first dehydration tower feed. The mixed stream S2 then enters the first dehydration distillation tower T1. In the first dehydration distillation tower T1, light components such as water accumulate at the top of the tower, and the separated water can be drawn off from the top. NMP and heavy components are at the bottom of the tower, and the dehydrated material can be drawn off from the bottom and enters the first product purification tower for further separation. Ethanolamine is enriched in the middle and upper section of the tower and can be drawn off from the side stream for subsequent reaction-distillation processes.

[0116] Specifically, the stream S3 from the top of the first dehydration distillation column T1 is condensed into stream S4 in the first dehydration column condenser E2 and enters the first dehydration column reflux tank V1. The gas stream S5 is further cooled by the first dehydration column vacuum collector E3. After cooling, the non-condensable gas stream S6 is extracted by the vacuum system configured in the first dehydration distillation column. The working pressure of the first dehydration distillation column T1 is controlled by the regulating valve on stream S6. Stream S7 flowing out of the first dehydration column reflux tank V1 is pressurized by the first dehydration column reflux pump P1 and then divided into two streams. One stream S8 returns to the first dehydration distillation column T1 as the reflux liquid phase of the first dehydration distillation column T1. The flow rate of stream S8 can be controlled by detecting the temperature of the sensitive plate of the first dehydration distillation column T1. The other stream S9 is discharged from the system as light component water (mainly water, with the remainder being some light components from NMP decomposition). The flow rate of stream S9 is controlled by detecting the liquid level in the first dehydration column reflux tank V1. The stream S26 from the bottom of the first dehydration distillation column T1 splits into two streams. One stream passes through the reboiler E1 of the first dehydration column, where a portion of the material is vaporized. The partially vaporized material S27 returns to the first dehydration distillation column T1 as the reboiler gas phase. The flow rate of the heating medium (steam or heat transfer oil) in the reboiler E1 can be controlled by detecting the temperature at the bottom of the column. The other stream S26 is transported to the first product refining column T3 via the heavy component discharge pump P2, serving as the feed stream S28 to the first product refining column T3. The flow rate of S28 can be controlled by the liquid level at the bottom of the first dehydration distillation column T1. The side stream S10 of the first dehydration distillation column T1 is drawn from the side stream of the first dehydration distillation column T1. Compared with the feed liquid S1 of NMP, the water content of the side stream S10 of the first dehydration distillation column decreases from about 20% to 1-3%, and the mass fraction of ethanolamine increases from 0.2-0.4% to 8-30%.

[0117] The first dehydration distillation column T1 has an operating temperature of 39–46℃ at the top and 130–135℃ at the bottom. The operating pressure at the top is 7–10 kPa. The column is packed with three layers of metal wire mesh packing. The first layer of packing is equivalent to 4–8 theoretical plates, the second layer is equivalent to 6–12 theoretical plates, and the third layer is equivalent to 10–24 theoretical plates.

[0118] The side stream S10 of the first dehydration distillation column is pressurized by the side stream pump P3 and then analyzed online using an online titrator or online gas chromatograph to control the amount of maleic anhydride added as a reactant. The ratio of the amount of maleic anhydride added to the amount of ethanolamine measured in stream S11 is controlled between 0.3 and 0.7 for the following reasons: 1. Since the boiling point of maleic anhydride is close to that of NMP, maleic anhydride cannot be added in excess, considering the subsequent separation of NMP and maleic anhydride; 2. Maleic anhydride may react with water to form maleic acid, which can corrode equipment, so maleic anhydride cannot be added in excess; 3. The reaction rate between maleic anhydride and ethanolamine decreases as the conversion rate increases. Maintaining a high conversion rate requires a larger reactor, increasing manufacturing costs, so the amount of maleic anhydride should not be too large; 4. If the amount of maleic anhydride added is too small, the concentration of ethanolamine returned to the first dehydration distillation column T1 will increase, resulting in increased distillation separation costs.

[0119] The reaction equation is as follows:

[0120]

[0121] In the first dehydration distillation column T1, the stream S10, relative to the feed S1, increases the concentration of reactants and the probability of intermolecular collisions, which is beneficial for increasing the reaction rate and the concentration of reaction products, thus reducing the energy consumption of subsequent separation. Furthermore, this reaction is exothermic, and the reaction system temperature has a significant impact on the reactant conversion rate. At too low a reaction temperature, the intermolecular collision rate is slow, making the reaction difficult to occur. At too high a reaction temperature, the acid anhydride is prone to hydrolysis (if the material has a high water content), and the alkene bonds in the acid anhydride molecules are also prone to self-polymerization, leading to side reactions. This reaction needs to be controlled at 120℃~135℃; the reaction pressure should not be lower than 25KPa, otherwise ethanolamine, or under low pressure conditions, will volatilize at high temperatures, reducing the reaction yield. The first reaction separation column T2 in this system controls the bottom temperature to not exceed 140℃, and the system pressure to be controlled at 1~5KPa. If the system pressure is higher, the temperature of the first reaction separation column will be higher, and the probability of NMP decomposition will be greater. Therefore, simply adding the reactants to the distillation column is not sufficient; a different approach is required. In this invention, the reaction feed stream S10 is pressurized by the dehydration tower side discharge pump P3. The pressurized stream S11 and the pressurized stream S12 (maleic anhydride) are mixed in the first reaction feed static mixer X2. The mixed stream S13 enters the first reaction and reaction separation tower reboiler E6 for reaction.

[0122] The features of the first reaction and reaction separation tower reboiler E6 are: 1. The first reaction and reaction separation tower reboiler E6 is similar to a shell-and-tube heat exchanger, but the difference is that an inner reaction heat exchanger tube is set inside the outer heat exchange tube of the original shell-and-tube heat exchanger. In addition to the inner tube sheet separating the shell side and the outer tube side of the heat exchanger, an outer tube sheet is also installed separating the outer tube side and the inner reaction heat exchanger tube side. This divides the equipment into three flow paths: the shell side carries the heat medium (steam or heat transfer oil); the outer tube side carries the stream S24, which requires reboiling at the bottom of the first reaction separation tower T2; and the inner reaction heat exchanger tube side carries the reaction stream S13. 2. The outer heat exchanger tubes are made of 25mm×2mm or 32mm×2mm stainless steel, while the inner reaction heat exchanger tubes are made of 10mm×1.5mm stainless steel. The stainless steel material can be 304 stainless steel, 304L stainless steel, 316 stainless steel, 316L stainless steel, etc. 3. The inner reaction heat exchanger tubes are internally reinforced heat exchanger tubes. This increases the disturbance and makes the material temperature inside the tube more uniform. On the one hand, the initial material in the inner reaction heat exchange tube is heated by the material in the outer heat exchange tube, which is conducive to quickly reaching the reaction temperature and accelerating the reaction rate. On the other hand, after the material in the inner reaction heat exchange tube reaches the reaction temperature, the heat generated by the reaction needs to be carried away by the material in the outer heat exchange tube, so that the material in the inner tube is maintained at 120℃~135℃. 4. The vaporization rate of the material in the outer heat exchange tube of the first reaction and reaction separation tower reboiler E6, which is a forced circulation reboiler, is controlled at 1.5~3%. This can control the temperature of the stream S23 in the reboiler to not exceed 135℃, and the stream S23 flows rapidly in the outer heat exchange tube, which is conducive to heat transfer and temperature control inside and outside the tube. 5. External heat exchange tubes are generally configured with two passes, while internal reaction heat exchange tubes are generally configured with two, four, or six passes. The more internal reaction heat exchange tubes, the longer the residence time of the material reaction and the higher the conversion rate, but the higher the equipment cost. 6. The pressure of the reactants inside the internal tubes should be greater than 25 kPa to ensure that ethanolamine does not volatilize and maintain a high reaction conversion rate.

[0123] The typical structure of the first reaction and the reboiler E6 of the reaction separation tower is shown in the figure. Figure 3 and Figure 4 ,in Figure 3 Both the inner and outer pipes are double-pass type, and steam is used as the heat transfer medium. Figure 4 The internal reaction heat exchanger has four tube passes, and the external heat exchanger has two tube passes. The heat transfer medium used is heat transfer oil.

[0124] Figure 3 In the diagram, N1 is the steam inlet, N2 is the condensate outlet, N3 is the inlet for the external heat exchanger tube material, N4 is the outlet for the external heat exchanger tube material, N5 is the inlet for the internal reaction heat exchanger tube material, and N6 is the outlet for the internal reaction heat exchanger tube material.

[0125] The first reaction and reaction separation tower reboiler E6 can be divided into three zones: Zone 1, the shell side of the equipment contains steam and condensate, the material in the outer heat exchange tubes is S23, and the material in the inner reaction heat exchange tubes is S13 and its reactants; Zone 2, the shell side of the equipment contains S23, the material in the inner reaction heat exchange tubes is S13 and its reactants; Zone 3, the shell side of the equipment contains S13 and its reactants.

[0126] Figure 4 In the diagram, N1 is the heat transfer oil inlet, N2 is the heat transfer oil outlet, N3 is the inlet of the external heat exchanger tube material, N4 is the outlet of the external heat exchanger tube material, N5 is the inlet of the internal reaction heat exchanger tube material, and N6 is the outlet of the internal reaction heat exchanger tube material.

[0127] The first reaction and reaction separation tower reboiler can be divided into three zones: Zone 1, the shell side of the equipment contains heat transfer oil, the material in the outer heat exchange tube is S23, and the material in the inner reaction heat exchange tube is S13 and its reactants; Zone 2, the shell side of the equipment contains S23, and the material in the inner reaction heat exchange tube is S13 and its reactants; Zone 3, the shell side of the equipment contains S13 and its reactants.

[0128] Figure 5 The diagram shows the structure of the internal and external heat exchange tubes. The characteristics of the heat exchange tubes are: 1. An internal reaction heat exchange tube is built into the external heat exchange tube; 2. The internal reaction heat exchange tube uses an enhanced heat and mass transfer tube, such as an internally threaded enhanced heat exchange tube or a spiral coil inserted inside the heat exchange tube; 3. If an internally threaded enhanced heat exchange tube is used, the bottom wall thickness is generally 0.25–0.3 mm, and the tooth height is generally in the range of 0.1–0.2 mm. Currently, the helix angle of the internally threaded tube is in the range of 15°–25°; 4. If a spiral coil is inserted inside the heat exchange tube, the spiral coil and the heat exchange tube are installed with a gap of 0.5–1 mm. A wire diameter d of 0.6–1.2 mm and a spiral pitch of 5–10 mm are selected; 5. A support is used between the external heat exchange tube and the internal reaction heat exchange tube. To prevent vibration, a support needs to be installed every 1 m–1.5 m.

[0129] The structural diagram of the support component is as follows: Figure 6 As shown, the support members for each section are arranged at 120°, with a total of three and the same length, to ensure that the center of the inner reaction heat exchange tube coincides with the center of the outer heat exchange tube. The contact point between the support member and the outer heat exchange tube is designed as an arc to ensure that the inner reaction heat exchange tube and the outer heat exchange tube can slide smoothly, which is convenient for installation and maintenance.

[0130] The reacted material stream S14 is drawn from the reboiler E6 of the first reaction and reaction separation tower and enters the first reaction separation tower T2. In the first reaction separation tower T2, light components such as NMP, unreacted ethanolamine, and a small amount of water generated by the reaction of maleic anhydride accumulate at the top of the tower and can be drawn back to the first dehydration distillation tower T1 for further separation of water, ethanolamine, and NMP; the reaction product of ethanolamine and maleic anhydride (N-(2-aminoethyl)maleimide), a small amount of NMP, and heavy components are at the bottom of the tower and can be drawn out of the boundary area. Specifically, the stream S15 at the top of the first reaction separation tower T2 is condensed into stream S16 in the condenser E4 of the first reaction separation tower and enters the reflux tank V2 of the first reaction separation tower. The gas stream S17 is further cooled by the vacuum trap E5 of the first reaction separation tower. After cooling, the non-condensable gas stream S18 is extracted by the vacuum system configured in the first reaction separation tower T2, and the working pressure of the first reaction separation tower T2 is controlled by the regulating valve on stream S18.

[0131] The stream S19 from the reflux tank V2 of the first reaction separation tower is pressurized by the reflux pump P5 and then split into two streams. One stream, S20, returns to the first reaction separation tower T2 as the reflux liquid phase. The flow rate of stream S20 can be controlled by detecting the temperature of the sensitive plate of the first reaction separation tower T2. The other stream, S21, is drawn from the top of the tower as the light component (NMP, unreacted ethanolamine, and a small amount of water generated from the reaction of maleic anhydride, etc.). It mixes with stream S1 and returns to the first dehydration distillation tower T1 to continue separating water, ethanolamine, and NMP. The flow rate of stream S21 is controlled by detecting the liquid level in the reflux tank V2 of the first reaction separation tower. The stream S22 from the bottom of the first reaction separation tower T2 is pressurized by the reboiler circulation pump P4 and split into two streams. One stream S23 passes through the reboiler E6 of the first reaction and reaction separation tower, where a portion of the material is vaporized. The partially vaporized material S25 returns to the first reaction separation tower T2 as the reboiler gas phase of the first reaction separation tower T2. The flow rate of the heat medium (steam or heat transfer oil) for heating the first reaction and reaction separation tower reboiler E6 can be controlled by detecting the temperature at the bottom of the tower. The other stream S24 mainly consists of the high-boiling-point product (N-(2-aminoethyl)maleimide) after the reaction of ethanolamine and maleic anhydride, a small amount of NMP, and heavy components, which is removed off-site as waste.

[0132] The first reaction separation tower T2 operates at a top temperature of 39–65°C and a bottom temperature of 125–135°C. The top operating pressure is 1–5 kPa. The tower is packed with two layers of metal wire mesh packing. The P4 packing layer is equivalent to 5–10 theoretical plates, and the P5 packing layer is equivalent to 5–10 theoretical plates.

[0133] The stream S28, which is supplied by the heavy component discharge pump P2 from the first dehydration tower to the first product refining tower T3, enters the first product refining tower T3. In the first product refining tower T3, NMP accumulates at the top and can be drawn off as the finished NMP product, while the bottom contains heavy components, which can be drawn off from the bottom and exit the boundary zone. The temperature at the top of this distillation tower is 85–105℃, which is less than 40℃ different from the temperature at the bottom (115℃–130℃). To save energy, a heat pump can be used to recover the heat of condensation from the top of the tower and raise its temperature to heat the reboiler. Specifically, the stream S29 at the top of the first product refining tower T3 is condensed into stream S30 in the condenser end of the first product tower heat pump E7 and enters the first product refining tower reflux tank V3. The gas stream S31 is further cooled by the first product tower vacuum trap E8. After cooling, the non-condensable gas stream S32 is extracted by the vacuum system configured in the first product refining tower. The working pressure of the first product refining tower is controlled by the regulating valve on stream S32.

[0134] The stream S33 flowing out of the reflux tank V3 of the first product refining tower is pressurized by the first product tower reflux pump P8 and then split into two streams. One stream, S34, returns to the first product refining tower T3 as the reflux liquid phase of the first product refining tower T3. The flow rate of stream S34 can be controlled by detecting the temperature of the sensitive plate of the first product refining tower T3. The other stream, S35, is drawn from the top of the tower as the NMP product. The flow rate of stream S35 is controlled by detecting the liquid level of the first product refining tower reflux tank V3. Meanwhile, the stream S36 at the bottom of the first product refining tower T3 is pressurized by the first product tower reboiler circulation pump P6, and then the stream S37 is partially vaporized by the heating end of the first product tower heat pump E7. The partially vaporized material S38 returns to the first product refining tower T3 as the reboiler gas phase of the first product refining tower T3. Another stream, S39, is drawn from the bottom of the first product refining tower T3. It mainly contains small amounts of NMP and heavy components. After being pressurized by the first product tower heavy component discharge pump P7, the stream S40 is moved to the outside as waste.

[0135] The first product refining tower T3 has an operating temperature of 85-105℃ at the top and 115-130℃ at the bottom. The operating pressure at the top is 2-4 kPa. The tower is filled with two layers of packing, which are metal wire mesh packing. The P6 packing layer is equivalent to 5-10 theoretical plates, and the P7 packing layer is equivalent to 5-10 theoretical plates.

[0136] The following is a specific implementation method: The mass fraction of NMP in the raw material waste liquid is 79.8%, the mass fraction of water is 19.6%, the mass fraction of ethanolamine is 0.4%, and the mass fraction of heavy components is 0.2%. The processing capacity is 1000 kg / hr. The ratio of the added molar flow rate of maleic anhydride to the molar flow rate of ethanolamine in the first reaction and the reboiler of the reaction separation tower is 30% to ensure complete reaction of maleic anhydride. Due to the partial pyrolysis of maleic anhydride, the actual ratio of the added molar flow rate of maleic anhydride to the molar flow rate of ethanolamine in the raw material waste liquid is approximately 103-110%.

[0137] The first dehydration distillation column T1 operates at a top temperature of 43℃, a bottom temperature of 131℃, and a top pressure of 8.5 kPa. The first reaction separation column T2 operates at a top temperature of 49℃, a bottom temperature of 133℃, and a top pressure of 1.5 kPa. The first product purification column T3 operates at a top temperature of 98℃, a bottom temperature of 122℃, and a top pressure of 3 kPa.

[0138] The first dehydration distillation column T1 has three layers of packing, using metal wire mesh packing. The first layer is equivalent to 5 theoretical plates, the second layer to 8 theoretical plates, and the third layer to 21 theoretical plates. The first reaction separation column T2 has two layers of packing, using metal wire mesh packing. Layer P4 and layer P5 are equivalent to 5 theoretical plates. The first product purification column T3 has two layers of packing, using metal wire mesh packing. The first layer and the second layer are equivalent to 5 theoretical plates.

[0139] The flow rate of the side stream S10 from the first dehydration distillation column is 100 kg / hr. The mass fractions of the substances in stream S10 are as follows: NMP 84.67%, water 2%, and ethanolamine 13.33%. Compared to the NMP feed solution, the water mass fraction decreased from 19.6% to 2%, while the ethanolamine mass fraction increased from 0.4% to 13.33%.

[0140] The flow rate of water from the top of the first dehydration distillation column T1 to the outside is 197.18 kg / hr, containing a small amount of NMP (1 ppm) and trace amounts of ethanolamine (<1 ppm) and light components from NMP decomposition (<1 ppm).

[0141] The flow rate of the reaction product from the bottom of the first reaction separation tower T2 to the outside is 11.75 kg / hr, containing the reaction product of ethanolamine and maleic anhydride (N-(2-aminoethyl)maleimide) and approximately 80% and 20% of the heavy components NMP.

[0142] The flow rate of heavy components at the bottom of the first product refining tower T3 to the outside of the tower is 4.27 kg / hr, of which NMP accounts for approximately 55%, and the remainder is heavy components.

[0143] The flow rate of the NMP product was 793.43 kg / hr, and the mass fraction of NMP was 99.99%, with the remainder being heavy components (1 ppm), trace water (<1 ppm), and trace ethanolamine (<1 ppm).

[0144] In terms of energy consumption, producing 1 ton of NMP product requires 1 ton of saturated steam at 130°C and 70 kWh of electricity.

[0145] The above results indicate that the final NMP yield reached 99.4%, and the ethanolamine in the NMP product could be controlled below 1 ppm, meeting the requirements for free amine in NMP used in some semiconductor industries.

[0146] In another embodiment, the removal of propanolamine from NPM wastewater feedstock using maleic anhydride is illustrated as an example:

[0147] A typical waste liquid contains 80% NMP, 19.4% water, 0.4% propanolamine, and 0.2% heavy components by mass. In lithium battery coating processes, an 80% NMP aqueous solution is commonly used, while the propanolamine mass fraction is typically 0.1%–0.4%. However, the apparatus of this invention does not strictly limit the specific component values; all components can be produced using the process of this invention. The entire system requires nitrogen or other inert gas for protection to prevent the oxidative decomposition of NMP.

[0148] The process is illustrated below using the typical waste liquid example described above:

[0149] The feed stream S101 is mixed with the stream S121 from the outlet of the reflux pump P15 of the second reaction separation tower in the static mixer X11 of the second dehydration tower feed. The mixed stream S102 then enters the second dehydration distillation tower T11. In the second dehydration distillation tower T11, light components such as water accumulate at the top of the tower, and the separated water can be drawn off from the top. NMP, propanolamine, and heavy components are at the bottom of the tower, and the dehydrated material can be drawn off from the bottom of the tower and enters the second product purification tower T13 for further separation. Specifically, the stream S103 from the top of the second dehydration distillation column T11 is condensed into stream S104 in the condenser E12 of the second dehydration column and enters the reflux tank V11 of the second dehydration column. The gas stream S105 continues to be cooled by the vacuum collector E13 of the second dehydration column. After cooling, the non-condensable gas stream S106 is extracted by the vacuum system configured in the second dehydration distillation column T11. The working pressure of the second dehydration distillation column T11 is controlled by the regulating valve on stream S106. The stream S107 flowing out of the second dehydration tower reflux tank V11 is pressurized by the second dehydration tower reflux pump P11 and then split into two streams. One stream, S108, returns to the second dehydration distillation tower T11 as the reflux liquid phase of the second dehydration distillation tower T11. The flow rate of stream S108 can be controlled by detecting the temperature of the sensitive plate of the second dehydration distillation tower T11. The other stream, S109, is discharged from the system as light component water (the main component is water, and the rest are some light components from NMP decomposition). The flow rate of stream S109 is controlled by the liquid level of the second dehydration tower reflux tank V11. The stream S126 from the bottom of the second dehydration distillation column T11 is divided into two streams. One stream passes through the reboiler E11 of the second dehydration column, where a portion of the material is vaporized. The partially vaporized material S127 returns to the second dehydration distillation column T11 as the reboiler gas phase. The flow rate of the heating medium (steam or heat transfer oil) in the reboiler E11 can be controlled by detecting the temperature at the bottom of the column. The other stream S126 is transported to the second product refining column T13 via the heavy component discharge pump P12, serving as the feed stream S128 to the second product refining column T13. The flow rate of S128 can be controlled by detecting the liquid level at the bottom of the second dehydration distillation column T11.

[0150] The second dehydration distillation column T11 has an operating temperature of 39–46℃ at the top and 130–135℃ at the bottom. The operating pressure at the top is 7–10 kPa. The column is packed with two layers of metal wire mesh packing. The first layer of packing is equivalent to 10–20 theoretical plates, and the second layer of packing is equivalent to 10–20 theoretical plates.

[0151] The side stream S110 near the bottom of the second product refining column is pressurized by the product column side stream pump P13. Online analysis using an online titrator or online gas chromatograph controls the amount of maleic anhydride added as a reactant. The ratio of the amount of maleic anhydride added to the molar amount of propanolamine measured in stream S111 is controlled between 0.3 and 0.5 for the following reasons: 1. Since the boiling point of maleic anhydride is close to that of NMP, and considering the subsequent separation of NMP and maleic anhydride, maleic anhydride cannot be added in excess; 2. Maleic anhydride may react with water to form maleic acid, which corrodes the equipment; therefore, maleic anhydride cannot be added in excess; 3. The reaction rate between maleic anhydride and propanolamine decreases as the conversion rate increases. Maintaining a high conversion rate requires a larger reactor, increasing manufacturing costs; therefore, the amount of maleic anhydride should not be too large; 4. If the amount of maleic anhydride added is too small, the concentration of propanolamine returned to the second dehydration distillation column T11 will increase, leading to increased distillation separation costs. (The reasons mentioned above are consistent with the operating conditions for removing ethanolamine), and the reaction equation is as follows:

[0152]

[0153] The side stream S110 of the second product refining column T13 is drawn from the liquid phase side stream of the lowest tray of the second product refining column T13. Compared with the feed liquid S101 of NMP, the water content of the side stream S110 of the second dehydration distillation column T11 decreases from about 20% to less than 1 ppm, and the mass fraction of propanolamine increases from 0.2-0.4% to 5-10%.

[0154] It can be seen that, compared to the raw material S101, the stream S110 in the second dehydration distillation column T11 increases the concentration of reactants and the probability of intermolecular collisions, which is beneficial to increasing the reaction rate and the concentration of reaction products, thus reducing the energy consumption of subsequent separation. Furthermore, this reaction is exothermic, and the temperature of the reaction system has a significant impact on the conversion rate of reactants. When the reaction temperature is too low, the intermolecular collision rate is slow, and the reaction is difficult to occur. When the reaction temperature is too high, the acid anhydride is prone to hydrolysis (if the material has a high water content), and the olefin bonds in the acid anhydride molecules are also prone to self-polymerization, thus causing side reactions. This reaction needs to be controlled at 120℃~135℃; the reaction pressure should not be lower than 15KPa, otherwise propanolamine or, under low pressure conditions, high temperature will cause it to volatilize, reducing the reaction yield. In this system, the pressure of the second reaction separation column T12 is controlled at 1~5KPa to ensure that the bottom temperature does not exceed 140℃. If the system pressure is higher, the temperature of the second reaction separation column will be higher, and the probability of NMP decomposition will be greater. Therefore, simply adding the reactants to the distillation column is not sufficient; a different approach is required. In this invention, the reactant stream S110 is pressurized via a side-stream discharge pump P3 from the dehydration tower. The pressurized stream S101 and the pressurized stream S112 (maleic anhydride) are mixed in the second reaction feed static mixer X12. The resulting mixed stream S113 then enters the second reaction and reaction separation tower reboiler E16 for further reaction. The characteristics of this second reaction and reaction separation tower reboiler E16 are the same as those of the first reaction and reaction separation tower reboiler E6 described above for the ethanolamine removal process, and will not be repeated below.

[0155] The post-reaction material stream S114 is drawn from the reboiler E16 of the second reaction and reaction separation tower and enters the second reaction separation tower T12. In the second reaction separation tower T12, light components such as NMP, unreacted propanolamine, and maleic anhydride react to form a small amount of water, which accumulate at the top of the tower and can be drawn back to the second dehydration distillation tower T11 for further separation of water, propanolamine, and NMP. The reaction product of propanolamine and maleic anhydride (N-(2-aminopropyl)maleimide), NMP, and a small amount of heavy components are at the bottom of the tower and can be drawn out of the boundary zone. Specifically, the stream S115 at the top of the second reaction separation tower T12 is condensed into stream S116 in the condenser E14 of the second reaction separation tower and enters the reflux tank V12 of the second reaction separation tower. The gas stream S117 is further cooled by the vacuum trap E15 of the second reaction separation tower. After cooling, the non-condensable gas stream S118 is extracted by the vacuum system configured in the second reaction separation tower. The working pressure of the second reaction separation tower T12 is controlled by the regulating valve on stream S118.

[0156] The stream S119 from the reflux tank V12 of the second reaction separation tower is pressurized by the reflux pump P15 and then split into two streams. One stream, S120, returns to the second reaction separation tower T12 as the reflux liquid phase. The flow rate of stream S120 can be controlled by detecting the temperature of the sensitive plate of the second reaction separation tower T12. The other stream, S121, is drawn from the top of the tower as the light components (NMP, unreacted propanolamine, and a small amount of water generated from the reaction of maleic anhydride, etc.). It mixes with the feed stream S101 and returns to the second dehydration distillation tower T11 to continue separating water, propanolamine, and NMP. The flow rate of stream S121 is controlled by detecting the liquid level in the reflux tank V12 of the second reaction separation tower. The stream S122 at the bottom of the second reaction separation tower T12 is pressurized by the reboiler circulation pump P14 and then split into two streams. One stream, S123, passes through the reboiler E16 of the second reaction and reaction separation tower, where a portion of the material is vaporized. The partially vaporized material, S125, returns to the second reaction separation tower T12 as the reboiler gas phase. The flow rate of the heat medium (steam or heat transfer oil) used for heating in the reboiler E16 can be controlled by detecting the temperature at the bottom of the tower. The other stream, S124, mainly consists of the high-boiling-point product (N-(2-aminopropyl)maleimide) from the reaction of propanolamine and maleic anhydride, NMP, and a small amount of heavy components, which is removed as waste and disposed of outside the boundary.

[0157] The second reaction separation tower T12 operates at a top temperature of 39–70°C and a bottom temperature of 125–135°C. The top operating pressure is 1–5 kPa. The tower is packed with two layers of metal wire mesh packing. The first layer of packing is equivalent to 5–10 theoretical plates, and the second layer of packing is equivalent to 5–10 theoretical plates.

[0158] The stream S128, which is supplied by the heavy component discharge pump P12 from the second dehydration tower to the second product refining tower T13, enters T13. In the second product refining tower T13, NMP accumulates at the top and can be drawn off as the finished NMP product. The bottom of the tower contains NMP, a small amount of heavy components, and a small amount of propanolamine; these bottom components are drawn off from the bottom and exit the boundary zone. The temperature at the top of this distillation tower is 75–95°C, within 40°C of the temperature at the bottom (105–115°C). To save energy, a heat pump can be used to recover the heat of condensation from the top of the tower and raise its temperature to heat the reboiler. Specifically, the stream S129 at the top of the second product refining tower T13 is condensed into stream S130 in the condenser end of the heat pump E17 of the second product tower and enters the reflux tank V13 of the second product refining tower. The gas stream S131 is further cooled by the vacuum trap E18 of the second product refining tower. After cooling, the non-condensable gas stream S132 is extracted by the vacuum system configured in the second product refining tower. The working pressure of the second product refining tower T13 is controlled by the regulating valve on stream S132.

[0159] The stream S133 flowing out of the reflux tank V13 of the second product refining tower is pressurized by the second product tower reflux pump P18 and then split into two streams. One stream, S134, returns to the second product refining tower T13 as the reflux liquid phase of the second product refining tower T13. The flow rate of stream S134 can be controlled by detecting the temperature of the sensitive plate of the second product refining tower T13. The other stream, S135, is drawn from the top of the tower as the NMP product, and its flow rate is controlled by the liquid level of the second product refining tower reflux tank V13. Meanwhile, the stream S136 at the bottom of the second product refining tower T13 is pressurized by the second product tower reboiler circulation pump P16, and then the stream S137 is partially vaporized by the heating end of the second product tower heat pump E17. The partially vaporized stream S138 returns to the second product refining tower T13 as the reboiler gas phase of the second product refining tower T13. Another stream, S139, is drawn from the bottom of the second product refining tower T13. Its main components are NMP and a small amount of heavy components. After being pressurized by the heavy component discharge pump P17 of the second product tower, stream S140 is moved to the outside as waste.

[0160] The second product refining tower T13 has an operating temperature of 75-95℃ at the top and 105-115℃ at the bottom. The operating pressure at the top is 1-2.5 kPa. The tower is filled with two layers of metal wire mesh packing. The first layer of packing is equivalent to 20-36 theoretical plates, and the second layer of packing is equivalent to 20-36 theoretical plates.

[0161] The following is a specific implementation method: The raw material waste liquid contains 80% NMP, 19.4% water, 0.4% propanolamine, and 0.2% heavy components. The processing capacity is 1000 kg / hr. The ratio of the added molar flow rate of maleic anhydride to the molar flow rate of propanolamine in the second reaction and the reboiler of the reaction separation tower is 30% to ensure complete reaction of maleic anhydride. Due to the partial pyrolysis of maleic anhydride, the actual ratio of the added molar flow rate of maleic anhydride to the molar flow rate of propanolamine in the raw material waste is approximately 103-110%.

[0162] The second dehydration distillation column T11 operates at a top temperature of 43℃, a bottom temperature of 131℃, and a top pressure of 8.5 kPa. The second reaction separation column T12 operates at a top temperature of 66℃, a bottom temperature of 134℃, and a top pressure of 1.5 kPa. The second product purification column T13 operates at a top temperature of 75℃, a bottom temperature of 106℃, and a top pressure of 1 kPa.

[0163] The second dehydration distillation column T11 has two layers of packing, using metal wire mesh packing. The first and second layers of packing are equivalent to 12 theoretical plates each. The second reaction separation column T12 also has two layers of packing, using metal wire mesh packing. The first and second layers of packing are equivalent to 5 theoretical plates each. The second product purification column T13 also has two layers of packing, using metal wire mesh packing. The first and second layers of packing are equivalent to 35 theoretical plates each.

[0164] The flow rate of the side stream S110 from the second product refining tower is 100 kg / hr. The mass fractions of the substances in stream S110 are as follows: NMP 88.29%, propanolamine 9.97%, water trace (<1 ppm), and the remainder heavy components. Compared to stream S101 containing NMP, the water mass fraction decreased from 19.4% to <1 ppm, while the propanolamine mass fraction increased from 0.4% to 9.97%.

[0165] The flow rate of water from the top of the second dehydration distillation column T11 to the outside is 194.71 kg / hr. Its composition is water, and it also contains trace amounts of NMP (<1 ppm), propanolamine (<1 ppm), and light components from the decomposition of NMP (<1 ppm).

[0166] The flow rate of the reaction product from the bottom of the second reaction separation tower T12 to the outside is 8.93 kg / hr. The reaction product contains approximately 68.8% propanolamine and maleic anhydride (N-(2-aminoethyl)maleimide), approximately 20.9% heavy components, approximately 5.5% NMP and approximately 4.8% propanolamine.

[0167] The flow rate of heavy components at the bottom of the second product refining tower T13 to the outside of the tower is 5 kg / hr, with NMP accounting for approximately 82.9%, propanolamine accounting for approximately 11.8%, and the remainder being heavy components.

[0168] The NMP product had a flow rate of 795.37 kg / hr and a mass fraction of 99.99%, with the remainder being water (11 ppm) and propanolamine (1 ppm).

[0169] In terms of energy consumption, producing 1 ton of NMP product requires 1.05 tons of saturated steam at 130°C and 160 kWh of electricity.

[0170] The above results show that the yield of the obtained NMP product reaches 99.4%, and the propanolamine in the product NMP can be controlled at 1 ppm, which meets the requirements of some semiconductor industry NMP for free amine.

[0171] In summary, the present invention provides a system for removing alkanolamines from NMP. Through the coordinated operation of three distillation columns, a reaction column, a reaction separation column, a reboiler, and other supporting equipment, optimal conditions for the reaction between acid anhydride and alkanolamines in NMP are designed. The reaction process is simultaneously coupled with the distillation separation process, which increases the reaction rate, reduces the occurrence of side reactions, and improves the reaction yield. The alkanolamine content in the product NMP can be controlled below 1 ppm, meeting the requirements for free amines in NMP used in some semiconductor industries. This invention achieves a system for removing alkanolamines from NMP with high yield, fast reaction rate, and energy saving.

[0172] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A system for removing alkanolamines from NMP recovery solution, characterized in that, This includes a dehydration distillation column, a reaction separation column, a product purification column, and a reaction and reaction separation column reboiler that serves as a reactor; The dehydration distillation column is connected to the reaction separation column and the product purification column, respectively. The reaction and reaction separation tower reboiler includes an external heat exchange tube; The external heat exchange tube contains an internal reaction heat exchange tube. The internal reaction heat exchanger tube is an internally enhanced heat exchanger tube; The reaction and reaction separation tower reboiler is provided with an inner tube sheet separating its shell side and outer heat exchange tube side, and an outer tube sheet separating its outer heat exchange tube side and inner reaction surrounding tube side. The external heat exchange tube of the reboiler of the reaction and reaction separation tower is connected to the reaction separation tower; When ethanolamine is removed, the internal reaction heat exchange tube of the reaction and reaction separation tower reboiler is connected to the dehydration distillation tower; When removing propanolamine, the internal reaction heat exchange tube of the reaction and reaction separation tower reboiler is connected to the product purification tower.

2. The system for removing alkanolamines from NMP recovery solution according to claim 1, characterized in that, Support members are provided axially at intervals of 1m to 1.5m between the external heat exchange tubes of the reaction and reaction separation tower reboiler and the internal reaction heat exchange tubes.

3. The system for removing alkanolamines from NMP recovery solution according to claim 2, characterized in that, The external heat exchange tubes of the reaction and reaction separation tower reboiler are concentrically arranged with the internal reaction heat exchange tubes; the support members are evenly distributed in the radial direction of the external heat exchange tubes.

4. The system for removing alkanolamines from NMP recovery solution according to claim 3, characterized in that, The support members are installed at 120-degree intervals in the radial direction of the external heat exchange tubes of the reaction and reaction separation tower reboiler.

5. The system for removing alkanolamines from NMP recovery solution according to claim 2, characterized in that, The position where the inner reaction heat exchanger tube support of the reaction and reaction separation tower reboiler contacts the outer heat exchanger tube is set in an arc shape.

6. The system for removing alkanolamines from NMP recovery solution according to claim 1, characterized in that, The internal enhanced heat exchange tube of the reaction and reaction separation tower reboiler is an internally threaded enhanced heat exchange tube or a spiral coil is inserted into the internal reaction heat exchange tube.

7. A system for removing alkanolamines from NMP recovery solution according to any one of claims 1 to 6, characterized in that, It also includes a static mixer for the feed to the dehydration tower; The top output of the reaction separation tower is connected to the first input of the static mixer for the feed of the dehydration tower. The second input terminal of the static mixer for the dehydration tower feed is used to connect NMP waste liquid raw material; The output end of the NMP waste liquid raw material is connected to the input end of the dehydration distillation column.

8. A system for removing alkanolamines from NMP recovery solution according to any one of claims 1 to 6, characterized in that, It also includes a side-line discharge pump, a reaction feed static mixer, an online titrator, a reaction feed flow controller, and a fourth regulating valve; The output end of the side-line discharge pump is connected to the first input end of the reaction feed static mixer; The detection point of the online titrator is connected to the pipeline between the output end of the side-line discharge pump and the first input end of the reaction feed static mixer. Based on the detection result, the control system calculates the set value of the reaction flow rate and adjusts the amount of acid anhydride substance input through the reaction feed flow controller and the fourth regulating valve. The second input terminal of the static mixer for reaction feed is used to input acid anhydride substances; The output end of the static mixer for the reaction feed is connected to the input end of the internal reaction heat exchange tube of the reboiler for the reaction and reaction separation tower, and the output end of the internal reaction heat exchange tube of the reboiler for the reaction and reaction separation tower is connected to the input end of the reaction separation tower. When removing ethanolamine, the side feed outlet of the dehydration distillation column is connected to the input end of the side feed pump; When removing propanolamine, the side stream outlet of the product refining tower is connected to the input of the side stream pump.

9. A system for removing alkanolamines from NMP recovery solution according to claim 8, characterized in that, When the acid anhydride is maleic anhydride and ethanolamine is removed, the ratio of the amount of maleic anhydride added to the amount of ethanolamine is in the range of [0.3, 0.7]. When the acid anhydride is maleic anhydride and propanolamine is removed, the ratio of the amount of maleic anhydride added to the amount of propanolamine is in the range of [0.3, 0.5].

10. A system for removing alkanolamines from NMP recovery solution according to claim 9, characterized in that, When the acid anhydride is maleic anhydride and ethanolamine is removed, the temperature of the reaction and the reboiler of the reaction separation tower is controlled at 120℃~135℃, and the reaction pressure is not lower than 25KPa. When the anhydride is maleic anhydride and propanolamine is removed, the temperature of the reaction and the reboiler of the reaction separation tower is controlled at 120℃~135℃, and the reaction pressure is not lower than 15KPa.

11. A system for removing alkanolamines from NMP recovery solution according to any one of claims 1 to 6, characterized in that, The reaction separation tower is filled with two layers of metal wire mesh packing. The first filler layer from top to bottom is equivalent to 5 to 10 theoretical plates, and the second filler layer is equivalent to 5 to 10 theoretical plates. When removing ethanolamine, the operating temperature at the top of the reaction separation column is 39℃~65℃, the operating temperature at the bottom of the column is 125℃~135℃, and the operating pressure at the top of the column is 1~5KPa; When removing propanolamine, the operating temperature at the top of the reaction separation column is 39℃~70℃, the operating temperature at the bottom of the column is 125℃~135℃, and the operating pressure at the top of the column is 1~5KPa.

12. A system for removing alkanolamines from NMP recovery solution according to any one of claims 1 to 6, characterized in that, When removing ethanolamine, the dehydration distillation column is filled with three layers of metal wire mesh packing. The first packing layer from top to bottom is equivalent to 4 to 8 theoretical plates, the second packing layer is equivalent to 6 to 12 theoretical plates, and the third packing layer is equivalent to 10 to 24 theoretical plates. When removing propanolamine, the dehydration distillation column is filled with two layers of metal wire mesh packing. The first packing layer from top to bottom is equivalent to 10 to 20 theoretical plates, and the second packing layer is equivalent to 10 to 20 theoretical plates.

13. A system for removing alkanolamines from NMP recovery solution according to claim 12, characterized in that, The operating temperature at the top of the dehydration distillation column is 39℃~46℃, the operating temperature at the bottom of the column is 130℃~135℃, and the operating pressure at the top of the column is 7~10KPa.

14. A system for removing alkanolamines from NMP recovery solution according to any one of claims 1 to 6, characterized in that, The product refining tower is filled with two layers of metal wire mesh packing. When removing ethanolamine, the first packing layer from top to bottom is equivalent to 5 to 10 theoretical plates, and the second packing layer is equivalent to 5 to 10 theoretical plates. The operating temperature at the top of the product refining tower is 85℃~105℃, the operating temperature at the bottom of the tower is 115℃~130℃, and the operating pressure at the top of the tower is 2~4KPa; When removing propanolamine, the first packing layer from top to bottom is equivalent to 20 to 36 theoretical plates, and the second packing layer is equivalent to 20 to 36 theoretical plates. The operating temperature at the top of the product refining tower is 75℃~95℃, the operating temperature at the bottom of the tower is 105℃~115℃, and the operating pressure at the top of the tower is 1~2.5KPa.

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